Acoustic device



Oct. 15, 1929. HALLAWELL 1,731,460

' ACOUSTIC DEVICE v Filed Sept. 26, 1928 Soon Rzswoust I IIVVE/VTOI? 'Fkmuzucx YcLssfs c. KaAZAHmI-Q //a ZwZL,

A ATTORNEY Patented Oct. 15, 192.9

UNITED STATES PATENT OFFICE AUSTIN MORRIS HALLAR'ELL, OF \VALLINGTON, ENGLAND, ASSIGNOR TO VICTOR TALKING MACHINE COMPANY, A CORPORATION OF NEW JERSEY ACOUSTIC DEVICE Application filed September 26, 1928, Serial No.

.The present invention relates to acoustic devices such for example as loud speakers and the like of the type in which the diaphragm or other sound producing or receiving surface is substantially unthrottled. That is to say the diaphragm is either adapted to operate without a horn, or if a horn is used, the mouth opening of the horn is not appreciablysmaller than the area of the diaphragm.

If the characteristic curve of a loud speaker be plotted between sound energy output and frequency for a constant electrical input, it

will usually be found that thecurve, instead of being a straight line parallel to the frequency axis as it should be in the ideal case, has one-or more pronounced irregularities. The present inventionprovides means where'- by certain of these irregularities may be reduced or eliminated. This is accomplished according to the invention by arranging adjacent to but spaced from a part of the diaphragm a fixed surface.- In this way an air space is provided which is resonant to the frequency or range of frequencies at which it is P desired to increase the response of the device.

If desired, a plurality of such resonant air spaces co-operating with one diaphragm may be provided.

The invention will be described by way of example with reference to the accompanying drawings in which Figs. 1 and 2 are diagrammatic views in elevation and plan respectively of a loud speaker embodying the invention. Fig. 1 being a section on the line 11 of Fig. 2, and

.Fig. 3 is a diagram illustrative of the invention.

Referring to Figs. 1 and 2, a diaphragm 1 v of thin aluminum is stretched and clamped in known manner between two rings 2 and 3. Three radial arms 4 project inwards from the ring 3 and support (in a manner not shown) a magnet 5. having an annular air gap 6 in which is arranged a coil 7 attached to the diaphragm 1. Three radial arms 8 project from the ring 2 and are united above the centre of the diaphragm 1. and threaded through the arms 8 at their junction is an adjusting screw 9 provided with a lock nut 10. Upon the lower end, of the screw 9 is tired a 308,367, and in Great Britain October 4, 1927.

disc 11. Three further adjusting screws 12, provided with lock nuts 13, are arranged in the radial arms 8 and these three screws support an annular ring 14. The screws 12 engage with the ring 14 and are adapted to 1'0- tate but not totranslatc relatively thereto.

Fig. 3 shows the response characteristic of a loud speaker, of the type above described, before and after correction with the aid of the present invention, the dotted line representing the uncorrected curve. The loud speaker has two dips in its response curve reaching maxima at about 1,600 and 300 cycles per second respectively.

In orderto remove or reduce the dip at 1,600 cycles per second the screw 9 is adjusted until the resonance due to the air space between the disc 11 and the diaphragm 1 is at 1,600 cycles per second. If the amount of correction provided is too small, the size of the disc should be increased and vice versa. hen the right adjustment has been foundthe screw 9 is locked by means of the nut 10. In one actual case to produce a correcting resonance at 1,600 cycles per second an air space one-tenth of an inch long was found to be suitable.

In order to produce a correcting resonance at 300 cycles per second the annular ring 1% is adjusted by means of the screws 12 which are then locked by means of nuts 13. A suitable length of air space was in practise found to be from 1 inch to 1 inches.

The correcting device may take the form of flat-plates as described above, or alternately it may consist of a solid body of any desired shape, provided that the surface thereof adjacent the diaphragm lies generally parallel thereto. It may be made of any suitable materiai, such for example as metal, wood or moulded material and it may be constructed with or without an aperture through the centre.

Although the invention has-been described as applied to a plane membrane it is not so limited but maybe applied equally to membranes, diaphragms or pistons of any shape. In general the effective surface of the correcting device would then conform roughly to the shape of the membrane, diaphragm or piston.

1,73 race Preferably, as described, where the drive a portion of said diaphragm, and means for is central and where more than one correcting adjustably mounting said devices for indedevice is used, the one providing resonance pendent adjustment toward and away from at the highest frequency is the central one, said diaphragm. since the higher the frequency of vibration, In te tim ny f' t' 1 gn my the more does the vibration of the diaphragm 11111110 to H115 speclficatwni become confined to the central portion there- AUSTIN MORRIS HALLrUNELL. of. in order to produce a flatter resonance, that is to say one covering a wider band of 1G frequencies, the air space may be made to i '15 vary progressively in depth.

Although means have been described for correcting two dips in the response curve it will be clear that any desired number of I 15 correcting devices may be used within the scope of the present invention.

I claim: 1. An acoustic device comprising :1 diaphragm or other sound producing or rccciv- 2() ing surface which is substantially unthrottled,

wherein a fixed surface is arranged adjacent to but spaced from a part of said diaphragm substantially as and for the purpose described.

5 2. A device as claimed in claim 1, wherein said diaphragm is flat and wherein said fixed surface is in the form of a disc.

3. A device as claimed in'claim 1, wherein said diaphragm is flat and wherein said fixed 30 surface is of annular shape.

-l-. An acoustic device comprising av .diaphrag'in which is substantially unthrottled, a device forming a fixed surface adjacent to but spaced from a part of said diaphragm,

5 and means for supporting said device with said surface spaced from said diaphragm.

5. An acoustic device comprising a diaphragm which is substantially unthrottled, a

support for the diaphragm, adevice con- AG stituting a surface adjacent to but out of con- 5 tact with a part of said diaphragm, and

means for mounting; said device on said diaphragm support with said surface in fixed relation to said diaphragm.

45 6. A device as claimed in claim 4, includw ing means for adjusting the fixed surface toward and away from the diaphragm.

7. An acoustic device comprising a diaphragm, a support therefor, a device torm- 50 inc a fixed surface arranged adjacent to but spaced from a part of said diaphragm, and means for adjustably mounting said device on said support. I

S. An acoustic device comprising a diaphragm, means forming afixed surface adjacent to out spaced from a part of said dia- 'phrag'm, an adjustable mounting for 'said' means whereby the position of said surface may be adjusted toward or away from said diaphragm, and means for locking said 1 5 mounting to prevent movement of said suri'ace from its adjusted position.

9. An acoustic device comprising a diaphragm, a plurality of devices each forming a fixed surface adjacent to but spaced from 9 

